Workers carefully guided a 15,000-pound, angled plate of steel into position Friday to serve as the keel for yet-another ocean-going exploratory oil rig built by LeTourneau Technologies in Vicksburg.

Placing the 60-foot-by-30 foot base is the initial phase of building the third in a class of rigs specifically for exploring in deep water and challenging conditions, LeTourneau vice president Mike Gray said.

“The machinery deck and the main deck will be built above the keel,” Gray said, adding the full rig will measure 225 feet by 200 feet.

The first in the 240C class of rigs, dubbed the Rowan Mississippi, floated down the Mississippi River in July and will be used in the Gulf of Mexico. Once built, the keel laid for the still-unnamed rig will be walked to the river in June 2010, Gray said, adding a twin rig, dubbed the Ralph Coffman, is about 42 percent complete and will leave the shipyard in June 2009.

Rigs of the Workhorse 240C class are designed to drill in water up to 400 feet deep and are larger than its predecessor, the so-called Tarzan, used in depths 350 feet or shallower. Both can bore 40,000 feet below the sea floor.

Those and previous rigs have found their way to oil deposits around the globe, including the oil-rich areas off Saudi Arabia and the Mexican state of Campeche.

When work is completed at LeTourneau’s west of U.S. 61 South here, mounds of dirt are placed under the rigs to allow the rig to “walk” off the river bank. Once afloat, most have the rest of the support legs installed at Sabine Pass in Texas.

Renewed activity at the plant this summer represents a foundation in itself. Operations ceased at the riverside south Warren County plant for more than a month following floods on the Mississippi River in April and May. Nearly all of its 1,100 employees were laid off while the water receded and work began to start repairs to badly damaged LeTourneau Road.

“We pretty much got them all back,” Gray said of the company’s work force, of which about 750 are employed by its Houston-based parent, Rowan Companies Inc., with the rest being contract hires.

Warren County was approved for more than $2.1 million in federal erosion-control grant money to shore up the eastbound lane of the access road. A local match will make up the balance of funding.

Among Vicksburg’s largest employers, LeTourneau began as a munitions plant in 1944. Over time, it evolved into a global leader for building movable oil rigs. Rowan acquired the yard from Marathon Inc. in 1994 after a two-year shutdown, and it reopened in September 1995.

The company’s founder, R.G. LeTourneau, invented the electric motor technology that allows the rigs’ legs to be lowered to the sea floor and then push the drilling platform above the waves. In essence, the technology makes the giant rigs portable.